Electrical heat exchanger



Sept. 27, 1966 w. A. CHURCHILL 3,275,801

ELECTRICAL HEAT EXCHANGER Original Filed June 17, 1964 FIG.2

FIG. 3 4 4 FIG. 4

INVENTOR WALTER A. CHURCHILL United States Patent 3,275,801 ELECTRICAL HEAT EXCHANGER Walter A. Churchill, 4 Hillcrest Road, Danvers, Mass. Original application June 17, 1964, Ser. No. 375,793, now Patent No. 3,168,775, dated Feb. 9, 1965. Divided and this application Dec. 9, 1964, Ser. No. 417,120 2 Claims. (Cl. 219-457) This application is a division of Patent No. 3,168,775, filed June 17, 1964, by Walter A. Churchill, the latter being a continuation-in-part of application Ser. No. 162,642, filed December 28, 1961, now abandoned.

The present invention relates to a heat exchanger and to the method of making it.

Heat exchangers of the prior art comprises a supporting member and a cylindrical electrical heater, the supporting member being made of metal and being cast about the heater. It has been found that the active life of these prior art exchangers has been considerably shortened due to comparatively early burning-out of portions of the cylindrical heater. Applicant has found that such burning-out is caused by lack of contact between portions of the cylindrical heater and such surrounding material, thus causing voids. Since the presence of such voids prevents the adequate transfer of heat from the heater there occurs a build-up of temperature at the portions of the element where these voids occur to such a degree that burn-out ensues. The heat exchanger of the present inventon is of a construction in which the foregoing difficulties are obviated.

The object of the present invention is the provision of a heat exchanger in which heat-exchanging contact is maintained between a heater and its heat-conducting support along the entire length of the part of the heater received in such support.

A further object is the provision of a heat exchanger comprising a heatconducting metallic base or supporting member with a groove therein, a cylindrical electrical heater in the groove the walls of the groove closely embracing the heater throughout the portion thereof received in the groove.

A still further important object is the provision in a heat conducting supporting member of a heater received in a groove having a cross-sectional dimension greater than that of the open side of the groove, the walls of the groove not only embracing the heater to a degree preventing accidental displacement from the groove but also being in uninterrupted intimate contact with the heater throughout the entire length of the groove.

A still further important object is the provision of a heat exchanger comprising a base of supporting member having a groove therein including an arcuate section terminating in two parallel terminal sections, the arcuate section extending throughout most of the circumference of a circle, and being thereby adapted to transfer heat from a heater in the groove in paths of substantially equal length from the groove to the center of the area enclosed thereby, so that the heating effect for this area is equally distributed.

Still another important object achieved by the present invention is the provision of an improved method of making a heat exchanger by establishing a cylindrical electrical heater in a particularly formed groove of a heatconducting base or support by a hammering action designed to assure uninterrupted intimate contact between the heater and the groove throughout the length of the latter.

A further important object is that of a method of securing a cylindrical electrical heater having a metallic casing in a heat conducting base member having a groove comprising the steps of enlargement of the cross-sectional area of parts of the groove spaced from the groove edges,

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disposing the cylindrical electrical heater in the groove and applying pressure to the heater to deform it so that its casing is in uninterrupted tight-fitting engagement with the enlarged portion of the groove throughout its length.

Other important objects of the invention will be apparent from the disclosures in the specification and in the accompanying drawings in which FIGURE 1 is a partial perspective view of the grooved base plate prior to its modification.

FIGURE 2 is a transverse sectional view of the grooved base plate illustrating the operation of undercutting the groove in the plate.

FIGURE 3 is an enlarged fragmentary sectional view showing the insertion of the heater.

FIGURE 4 is a fragmentary sectional view similar to FIG. 3 showing the application of a hammer tool to the electrical heater.

FIGURE 5 is a fragmentary sectional view showing the relationship of the casing of the heater and the walls of the groove upon completion of the hammering operation.

FIGURE 6 is a perspective view of the finished article.

With reference to the drawings in greater detail, FIG- URE 1 shows a partial perspective view of the supporting member 1 which may be made of a cast malleable metal, for example an aluminum alloy. The member 1 is cast with the groove 2 which comprises arcuate section or circular grooves 7 terminating in spaced parallel portions or grooves 8, the groove being processed to accommodate therein an electrical heater as more part-icularly shown in FIGURE 6.

Applicants method of securing the heater in the supporting member 1, comprises as a first step, the modification of the groove 2. As shown in FIGURE 2, this modification involves the undercutting of the opposite side walls of the groove by a suitable tool 3, for example, a rotary grinding tool. This is inserted in the groove and is employed to undercut opposite walls thereof throughout their length. Each of these walls is undercut to a height from the bottom of the groove greater than onehalf the height of the uncut groove. Exemplary groove dimensions may be as follows: In the supporting member 1 as cast, the groove may be /2" wide and /2" deep. This width is increased to /2"+.0l5 or .515" by the undercutting process. As shown in FIGURE 2, the undercutting operation forms opposite cut-away portions or cavities 2' having walls merging with the bottom portion of the groove and forming shoulders 6 with the uncut portions 2" of the groove walls. The portions or cavities 2' of the arcuate portion 7 of the groove 2 curve in two mutually transverse directions; i.e., in directions to conform to the arc of the arcuate portion and in directions upwardly from the bottom of the groove.

Applicants second step, illustrated by FIGURE 3, comprises the insertion into the open side of groove 2 of an electrical cylindrical heater 4 of a type wall known in the art consisting for example of metallic tubular casing or sheathing 4 enclosing insulation material 4" surrounding a helically wound electrical resistance wire 4" such as shown in Norton 2,875,312, the heater 4 having a diameter of approximately the width of the uncut portions 2" of the groove 2 and a length somewhat greater than the length of the groove. The heater 4 is then passed through the uncut portions 2 of the groove downwardly until it is received in the undercut portions 2' and rests along the bottom of the groove.

The third step in applicants method is shown in FIG- URE 4 and comprises the application of successive reshaping blows administered to the heater 4. These blows are applied to substantially the entire length of the exposed upwardly facing portion of the casing of the heater by a hammer tool 5 inserted through the open side of the groove 2. The effect of these blows is to cause the heater to be deformed so that side portions of the casing 4 intimately and continuously engage the cut-away portions or cavities 2 of the groove walls throughout their entire length, the deformation entailing a flattening of the upper portion of the heater 4 sustaining the hammer blows.

The relationship of the heater to the walls of the cutaway groove portions 2' and of the uncut groove portions 2" is shown in FIG. 5.

The finished article produced by applicants method is shown in FIGURE 6, the base or supporting member 1 having a groove therein comprising arcuate and parallel sectionsor grooves 7 and 8 respectively, all of these groove sections having the cross-sectional form shown in FIG. 5. The heater 4 is disposed in the groove sections in the relationship with the walls thereof as shown by the latter figure and according to the method previously described. This manner of disposal as said before, insures such continuous and intimate cont-act between the cut-away portions 2' of the groove and the heater as to maintain a homogenous heat exchange relationship throughout the contacting lengths of the groove and the heater, there being a complete absence of voids therebetween.

The end portions of the heater as shown, protrude from the ends of the parallel groove sections and, if desired, may be provided with conventional terminals.

As will be apparent, not only will the heater 4 be in intimate and continuous contact along the lengths of the cut-away portions 2' after the hammering operation, but the shoulder portions 6, comprising the intersecting walls of the cut-away portions 2' and the uncut portions 2" of groove 2 will effectively prevent accidental dislodgement of the heater from the groove. As shown in FIGURE 5, the major portion of the heater 4 lies below the lower ends of the parallel walls 2", the upwardly facing fiat portion of the casing 4' of the heater being disposed be tween these walls.

It is to be understood that modifications and variations of the disclosed method and of the finished article may be resorted to without departure from the spirit and scope of the invention, such modifications and variations being considered to be within the purview and scope of the appended claims.

What I claim is:

1. A heat exchanger comprising a metallic base plate comprising an outer circular peripheral portion, said base plate having a circular groove therein including two terminal portions adjacent each other, two mutually adjacent parallel grooves in said base plate extendinginwardly from said outer circular peripheral portion and into said two terminal portions, an elongated electrical heater disposed in said circular groove and extending from said circular groove into said two mutually adjacent parallel grooves, said circular groove and said parallel grooves each comprising parallel walls, said walls as seen in crosssection being defined by rectilinear parallel lines, said circular groove and said two mutually adjacent parallel grooves further comprising oppositely disposed curved wall portions intersecting said parallel walls and forming shoulders therewith, said electrical heater being in continuous and intimate contact with said wall portions and with the bottoms of said circular groove and of said parallel grooves, said shoulders in said circular groove and in said two adjacent parallel grooves being effective to prevent accidental dislodgment of said electrical heater from each of said grooves.

2. A heat exchanger according to claim 1, wherein the end portions of said electrical heater protrude from said mutually adjacent parallel grooves.

References Cited by the Examiner UNITED STATES PATENTS 1,617,916 2/1927 Kercher et al 219-540 X 2,389,588 11/1945 Woodman 219-254 X 2,725,453 11/1955 Haller 219-254 X 2,910,570 10/1959 Bremer et al 219-455 X 2,987,300 6/1961 Greene 29-15563 X 3,110,796 11/1963 Bremer 219-457 FOREIGN PATENTS 656,485 2/1938 Germany. 485,098 5/1938 Great Britain.

RICHARD M. WOOD, Primary Examiner.

V. Y. MAYEWSKY, Assistant Examiner. 

1. A HEAT EXCHANGER COMPRISING A METALLIC BASE PLATE COMPRISING AN OUTER CIRCULAR PERIPHERAL PORTION, SAID BASE PLATE HAVING A CIRCULAR GROOVE THEREIN INCLUDING TWO TERMINAL PORTIONS ADJACENT EACH OTHER, TWO MUTUALLY ADJACENT PARALLEL GROOVES IN SAID BASE PLATE EXTENDING INWARDLY FROM SAID OUTER CIRCULAR PERIPHERAL PORTION AND INTO SAID TWO TERMINAL PORTIONS, AND ELONGATED ELECTRICAL HEATER DISPOSED IN SAID CIRCULAR GROOVE AND EXTENDING FROM SAID CIRCULAR GROOVE INTO SAID TWO MUTUALLY ADJACENT PARALLEL GROOVES, SAID CIRCULAR GROOVE AND SAID PARALLEL GROOVES EACH COMPRISING PARALLEL WALLS, SAID WALLS AS SEEN IN CROSSSECTION BEING DEFINED BY RECTILINEAR PARALLEL LINES, SAID CIRCULAR GROOVE AND SAID TWO MUTUALLY ADJACENT PARALLEL GROOVES FURTHER COMPRISING OPPOSITELY DISPOSED CURVED WALL PORTIONS INTERSECTING SAID PARALLEL WALLS AND FORMING SHOULDERS THEREWITH, SAID ELECTRICAL HEATER BEING IN CONTINUOUS AND INTIMATE CONTACT WITH SAID WALL PORTIONS AND WITH THE BOTTOMS OF SAID CIRCULAR GROOVE AND OF SAID PARALLEL GROOVES, SAID SHOULDERS IN SAID CIRCULAR GROOVE AND IN SAID TWO ADJACENT PARALLEL GROOVES BEING EFFECTIVE TO PREVENT ACCIDENTAL DISLODGEMENT OF SAID ELECTRICAL HEATER FROM EACH OF SAID GROOVES. 